👉 In the context of mathematics, a "dashy number" is a positive integer that can be written in the form $2^a - 1$, where $a$ is an integer greater than or equal to 3. For instance, consider the following numbers: - $5 = 2^1 - 1$ - $7 = 2^2 - 1$ These are "dashy" because they can be written in this form.